Can you return a phone to Apple that has been faulty (sound issues/since the day I bought it brand new if I just got a crackon the phone?
They may repair the sound issues under warranty but the cracked screen will stay cracked. Unless the product is brand new-ish, the majority of manufacturers/retailers now send high value products for repair rather than a direct replacement.
I don't think they would have a problem with that.
You can definitely claim under warranty. But Apple will charge you for a screen replacement, even if the my then choose to change the complete phone for a new of refurbished iPhone 8. Apple won’t even consider the warranty work until you pay for the screen replacement. If you paid for AppleCare Plus (accidental damage cover) then the screen replacement will be covered but you’ll still have to pay an excess/deductible. Note that if they determine the sound fault was also caused by accidental damage then you’ll end up paying for that repair as well unless the phone is insured. In future if you find a fault on a new item, contact the manufacturer immediately to make a warranty claim. Your problem is that even if the sound fault was there from the start it could now look as if it was caused by accidental damage.
You will pay to have the screen fixed as it is not their fault.